The discovery of new gas and oil deposits of low production capacity, located at variable depths and in zones presenting difficult development conditions, has led to use new technologies allowing the running costs to be reduced for these deposits. Thus, the use of conventional fixed platforms seems to be increasingly abandoned for lighter floating platforms which are used as intermediate stations for the transportation or transfer of the effluents.
Patent FR-2,665,725 and patent application EN-91/04,223 filed by the applicant teach to use floating systems for the transfer of multiphase effluents, without separation of their constituents, from a deposit towards a main treatment platform with the aid of pumping means positioned on the floating system or intermediate floating station. However, this method requires a sufficient pressure at the outlet of the immersed wellhead, not only to allow the effluent to flow up from the sea bottom towards the floating system, but also for the effluents to have thereafter a sufficient pressure level allowing the pumping means located on the intermediate floating station to communicate them a pressure increase enabling their transfer over a given distance from the intermediate station towards a treating station. The pressure of the effluent at the inlet of the pumping means depends on the characteristics of the well (very eruptive well or not) and also on the depth at which the deposit is located.
The devices described in the prior art cited above have practically no effect on the effluent, notably on the pressure drop occurring during its upflow between the well and the light structure.
It is therefore necessary to have a system and a method allowing this pressure drop to be compensated for.